Science Objectives for Everyone
The DEvice for the study of Critical LIquids and Crystallization (DECLIC) is used to study crystal growth in transparent liquids. The Directional Solidification Insert (DSI) portion of DECLIC observes clear alloys that freeze like metals in microgravity. By providing real-time views of the crystal structures that form in the liquid, DECLIC-DSI sheds light on the physics that control the formation of solid materials.

Science Results for EveryoneInformation Pending

The following content was provided by Nathalie Bergeon, Ph.D., Rohit Trivedi, Ph.D., and is maintained in a database by the ISS Program Science Office.

Previous investigations employed an organic alloy sample material (succinonitrile-camphor) that is used as a model for metallic alloy systems. The specific alloy composition for the reflight of the DSI is determined by ground-based experiments and phase-field numerical simulations informed by previous DSI flight-experiment results.

This investigation particularly focuses on the origin of sidebranches that occur when columnar solidification patterns transform from cellular to dendritic as a function of thermal gradient and solidification velocity and study the potential for the formation of an intermediate multiplet pattern.

The dynamics and stability of cellular and dendritic growth patterns, and the relationship between the tip geometry and growth pattern are to be investigated as well.

The main goal of the DSI-R investigation is to quantitatively establish the fundamental physics controlling the spatiotemporal organization of the secondary sidebranch structure and its interaction with the array structure of primary branches under directional solidification conditions. This investigation will directly address outstanding issues that remain open in the understanding of complex dendritic microstructures.

Description
The Directional Solidification Insert Reflight (DSI-R) investigation involves the study of directional solidification in relation to SCN-based bulk alloys (succinonitrile-a transparent organic substance in the liquid state that is used to study the phenomena related to solidification processes) and transparent model alloys. This includes investigating the birth and growth of morphological instabilities at the solid-liquid interface and the effects of coupling between the solidifying interface and areas of convection, through a systematic variation of process parameters such as temperature. By observing these phenomena in a microgravity environment, it is possible to refine the theoretical models and numerical simulation predictions, which ultimately results in an improvement of industrial ground-based material development processes. The goal of these reduced-gravity experiments on ISS is to obtain benchmark data on cellular and dendritic microstructure formation under diffusive transport conditions. This investigation directly addresses outstanding issues that remain open in the understanding of complex dendritic microstructures.

From an engineering point of view, the DECLIC hardware uses two International Space Station (ISS) program-provided lockers comprised of the lower locker called the ELectronic Locker (ELL), which houses power supplies, data handling and central regulation electronics for operation and control. This lower locker contains all necessary electrical and electronic systems that permit the facility to operate in an autonomous mode or with telescience interactions from the scientific team at the dedicated user center. The upper locker is the EXperiment Locker (EXL). It contains the DECLIC optical bench that receives the investigations cartridge insert which contains a specific scientific material being examined. This optical bench contains all optical and opto-electronic sensors that are necessary to perform measurements at low or high rate of acquisition.

The DECLIC DSI-R investigation is operated by the Central Regulation Electronics (CRE), located in the EXL of the DECLIC instrument. The CRE controls several functions such as: running thermal control algorithms; making a precision acquisition of temperature sensors used by the thermal control algorithm; supplying accurate electrical voltages to be width modulated by insert electronics for heating elements; controlling power to heating elements; controlling cartridge insert speed inside the furnace; and managing the safe status of the cartridge insert (i.e., to prevent overheating).

Precise measurement of interface shape and geometrical characterization of cellular and dendritic patterns, as well as of individual cell or dendrite is carried out as a function of time for different values of composition, growth rate and temperature gradient. These measurements are used in combination with modeling and numerical simulations of the temperature fields in order to establish the physics that govern the dynamics of interface pattern selection, and finally to quantitatively determine the conditions for the planar to cellular and cellular to dendritic transitions. Optical observations of the solidification front is done either directly or by interferometry (imaging using the interference fringes resulting from the recombination of reference and object light beams issued from the same coherent source) with the cartridge placed in one arm of a Mach-Zehnder interferometer (a device used to determine phase shifts caused by the solidifying sample which is placed in the optical path of the object beam).

Space Applications
Microgravity provides a unique environment for studying the crystallization of solid materials in multi-phase liquids. Crystals grown in space are larger and have fewer defects so ideal crystals may need to be grown in microgravity conditions.

Earth Applications
Studying these crystal forming events in space eliminates the influence of gravity, which leads to more accurate predictions and computer simulations. Crystal growth research in space helps to improve ground manufacturing, which make products through melting and solidifying materials.

Operational Requirements
After the DSI-R is installed by the crew, the DECLIC runs automatically following a timeline of sequences that are commanded by the payload control center (CADMOS in Toulouse, France). The data transmitted to ground by real time telemetry allows the investigation team to monitor the health and status. Yet, due to telemetry bandwidth limitations, the entire data set cannot be downlinked and is therefore copied to a Removable Hard Disk Drive (RHDDs) for future return to the ground. The data is then transferred and stored at the CADMOS operational center, and available for the research teams to process and review.

Operational Protocols
The ISS crew installs the DSI-R hardware into the DECLIC payload facility and then powers facility on. Crew participation is not required during investigation runs excepted for the changing out of full Removable Hard Disk Drives (RHDDs). Typically, once the DSI-R is inside DECLIC, the investigation consists of running several successive melting-solidification cycles over a specified period of time.